Lock PDF

How to password protect a PDF

Choose your PDF, type the password people will need to open it, repeat it, and press Lock PDF. The protected copy downloads straight away with “-protected” added to its name, and your original file is left untouched. Because the work happens in your browser, contracts, payslips, medical letters and ID scans never pass through a server, which is the safest way to protect a document you would not want a stranger to read.

What kind of protection is this?

The file is encrypted with AES-256 using the standard PDF security handler (PDF 2.0, revision 6). That is the same strength banks and governments rely on for documents, and without the password the contents cannot be read. Opening the file asks for the password in Acrobat, Chrome, Edge, Firefox, Safari and phone viewers alike.

Open password and owner password

The open password stops anyone from viewing the document at all. The owner password controls what a person may do after opening it, such as printing or copying text. The checkboxes set those limits, and a random owner password is created for you unless you enter your own. Many viewers honour the limits, but some tools ignore them, so rely on the open password when real secrecy matters.

Choosing a good password

1. Use twelve or more characters, or a phrase of several unrelated words.
2. Do not reuse a password from email, banking or social media.
3. Store it in a password manager, and send it to the recipient by a different channel than the file, such as a phone call or message.
4. Keep an unlocked original somewhere safe. A forgotten password cannot be recovered by anyone, including us.

Good to know

Locking does not change what your pages look like. A file that is already protected must have its old password removed first. After locking an important file, open it once and type the password to make sure it works before you send it.

Frequently asked questions

Is my PDF uploaded when I lock it?

No. The file is read, encrypted and saved inside your browser. Neither the PDF nor your password is sent to ConverterMaster or anyone else.

How strong is the protection?

The file is encrypted with AES-256, the strongest standard PDF encryption (PDF 2.0, revision 6). Anyone without the password cannot open it. The real limit is the password you choose: a long, unique one is far harder to guess than a short or common one.

What if I forget the password?

It cannot be recovered. ConverterMaster never sees or stores your password, and there is no reset. Keep the password in a password manager and keep an unlocked original in a safe place.

What are the permission options?

You can allow or block printing, copying text, editing and adding comments or filling forms. These limits are set by an owner password. Viewers such as Adobe Acrobat, Chrome, Edge and Preview respect them, but some tools ignore them, so treat them as a courtesy and not as security. Only the open password truly keeps people out.

Will it open on my phone and in other programs?

Yes in current versions of Adobe Acrobat and Reader, Chrome, Edge, Firefox, Safari, macOS Preview and iOS and Android viewers. Very old PDF software from before 2008 may not support AES-256.

Can I lock a PDF that already has a password?

Not here. Remove the old password first, then lock the file again with the new one.

Does locking change how my document looks?

No. Pages, fonts, images and links stay as they were. The file is rewritten and encrypted, and the page content itself is not altered. Bookmarks and form fields are normally kept, though complex files should be opened once after locking to check.

How large a file can I lock?

Up to 200 MB. Everything runs on your own device, so very large files can take a little longer on phones and older computers.

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